The present invention relates to units for distillation of a liquid product, primarily petroleum stock, and may be used in the petroleum refining industry for rectification of petroleum stock.
A unit for distillation of petroleum stock is known comprising a vacuum column and a vacuum-creating apparatus with a jet device--steam ejector (see, e.g. U.S. Pat. No. 2,105,935, class C 10 G 7/00, 1938).
A drawback of the known unit is that petroleum fractions are mixed with steam and, accordingly, a portion of the petroleum fractions are carried away with the steam, which results in contamination of the steam condensate and reduction of the efficiency of the unit.
The unit most similar to the proposed invention is a unit for distillation of a liquid product comprising a vacuum column with mains for supplying the liquid product and removing the vapor-gas phase and a vacuum creating apparatus including a jet device--a steam ejector, connected by its gas input to the vapor-gas phase removal main of the vacuum column (see, for example, the Handbook of a Petroleum Refiner, edited by G. A. Lastovkin, Leningrad, Khimiya, 1989, p. 74).
The necessary degree of the vacuum in the unit indicated above is achieved by an ejector-type steam pump in which steam is used as the ejecting (working) medium.
The steam mixes with petroleum vapors and decomposition gases which results in contamination of the steam condensate, and also results in a part of the petroleum fractions being carried away with the steam condensate. Furthermore, the ejector-type steam pump does not ensure compression of the hydrocarbon gases to the pressure required for supplying the gases, for example, into the fuel collector of a refinery. Therefore, such gases have to be burned in flares if an additional compressor is not provided. It should also be noted that the mutual positioning of elements of the unit relative to each other has a substantial effect on the operation of the unit. In particular, the position of the jet device and the pressure main in space and the height at which the jet device is positioned relative to other elements of the structure are important, since if the positioning of the aforesaid elements of the unit relative to each other is not optimum, this may result in a loss of the vacuum while the vacuum-creating apparatus is stopped, which will reduce the reliability of operation of the unit as a whole and make its utilization more difficult.
Another drawback of the known unit is the condensation of highly volatile fractions prior to the jet device in a cooler-condenser, which due to the pressure differential in the latter results in a higher pressure in the upper part of the vacuum column, and this reduces the degree of yield of highly volatile fractions or results in an increase of the power consumed for the creation of a vacuum in the vacuum column.